Total Phenolic Content, Antioxidant and Antibacterial Activities of Different Fractions or Sonneratia apetala (Buch.-Ham.) Fruit

Abstract

Plants are the most important source of bioactive compounds providing health benefits. The mangrove fruit Sonneratia apetala (Buch.-Ham.) is extensively consumed by the people of coastal Bangladesh, especially those adjacent to the Sundarbans forest. To seek out the potential source of bioactive compounds, free radical scavenging activity, antioxidant capacity, and antibacterial activities, different fractions of S. apetala (Buch.-Ham.) fruit (seed and pericarp) were studied. The solvents used for the fractionation were n-hexane, di-ethyl ether, chloroform, ethyl acetate, and methanol. Among the fractions, methanol (MS) extract of seed had the highest polyphenols (221.95 mg GAE/g extract) content, followed by di-ethyl ether (DS: 33.35 mg GAE/g) and ethyl acetate (ES: 29.36 mg GAE/g) extracts of seed, whereas methanol (MP) extract of pericarp had the lowest polyphenols (10.31 mg GAE/g) content. From the experiment, it was seen that MS showed the most potent DPPH radical scavenging activity with an IC₅₀ value of 4.38 μg/mL, followed by ES (30.37 μg/mL) and DS (38.23 μg/mL). MS showed 77.1% NO radical scavenging activity at 800 μg/mL with an IC₅₀ value of 415.20 μg/mL, followed by DS and MP with IC₅₀ values of 1431 and 2030.46 μg/mL, respectively. At 100 μg/mL, MS showed the highest absorbance (O.D. 1.672), followed by ES (O.D. 0.346) and DS (O.D. 0.321). At 200 μg/mL, chloroform (CS) extract of seed showed the highest metal (Fe²⁺) binding capacity (48.67%) followed by MS (42.67%) and n-hexane (HS) (40.13%) extracts of seed. The IC₅₀ values for CS, MS, and HS in chelating Fe²⁺ were 296.38, 498.01, and 396.83 μg/mL, respectively. Moreover, MS showed the highest total antioxidant capacity (183.34 mg AAE/g; 121.42 mg GAE/g). This was followed by DS (177.11 mg AAE/g; 117.31 mg GAE/g) and CS (157.36 mg AAE/g; 103.56 mg GAE/g). The antioxidant capacity was lowest in di-ethyl ether (DP) extract of pericarp (13.54 mg AAE/g; 8.96 mg GAE/g). In addition, MS inhibited the growth of Escherichia coli, Salmonella paratyphi A, Salmonella typhi, Shigella dysenteriae, and CS inhibited the growth of Vibrio cholera, whereas both of them inhibited the growth of Staphylococcus aureus. The IC₅₀ values for MS against E. coli, S. paratyphi A, S. typhi, S. dysenteriae, and S. aureus were 0.56 mg/mL, 0.2632 mg/mL, 1.8632 mg/mL, 0.847 mg/mL, and 1.0186 mg/mL, respectively. CS against S. aureus and V. cholera was 1.33 mg/mL and 1.02 mg/mL, respectively. MS completely inhibited the growth of E. coli, S. paratyphi A, and S. dysenteriae at 2, 1, and 2 mg/mL, respectively. In conclusion, the results showed that among the fractions, MS, DS, and CS are potential sources of bioactive compounds such as polyphenols and antioxidants, whereas MS and CS have potential antibacterial activities. Therefore, the fruits of S. apetala have activities beneficial to health.